Building a Raised Bed Keyhole Garden

As the cold wind howled outside, I was rattling around the confines of my home, going a little stir crazy. The winter of 2009 had been long and cold in Connecticut. Although the snow had melted by late March, frost still regularly visited overnight and I knew my desire to get out, and plant, wouldn’t be realized for several months. But, even if my lettuce and spinach couldn’t survive outside right now, the idea of being productive and doing something in my garden had taken hold of me.

But what could I do?

A thought had been growing in the back of my mind for several days: build a raised bed garden. It would be simple enough to just toss soil between some wooden slats, but I had something more permanent and aesthetically pleasing in my mind.

The Effectiveness of a Raised Bed Garden for Annual Planting

A few months before I’d stumbled upon the interesting work of Send A Cow, a British charity that works to bring sustainable, small-scale agriculture to African countries. Specifically I’d been inspired by how they address the harsh climatic conditions of Lesotho, where rain has just two modes: torrential downpours, and not at all.

The soil in Lesotho is infertile, rocky, and thin, and periods of intense heat and cold come and go. When land is cleared for planting it will dry and crack during the droughts and then be washed away by the relentless downpours. In short, the traditional clear and plant agricultural paradigm doesn’t work, even in a small-scale garden.

Send A Cow helps the locals from multiple African countries build raised bed keyhole gardens for their annual vegetables, with materials sourced from what is available locally, and with different designs to suit their respective climates. These raised beds allowed locals to stop soil from being washed away, keep the soil moist, and harvest a more regular crop. You can learn more about how they use raised bed gardens in Lesotho here:

While my problems were nowhere near as severe as those dealt with in Lesotho, my New England garden, despite being improved by several years of soil building, was still clayey and filled with rocks. I knew I could get a better yield with better soil.

Some further research told me that beginning around 300 B.C., the Quechuas of South America had deployed raised bed gardens to increase their yields while reducing soil erosion (1). Their system of raised beds and irrigation, which they called Waru Warn, brought about impressive results. It was successful enough that it’s still being used in Bolivia and Peru today.

By wrapping a circular raised bed garden around a "keyhole" walkway entrance, more space can be utilized. In a traditional garden bed, with single rows of plants interrupted by paths, you waste about half the garden space. With a raised bed garden with paths going between every three or four rows, you cut down the space wasted with walkways to about 30 percent. With a circular raised bed, less than a quarter of the ground is surrendered to paths (2).

I decided that the next day — which weather forecasters predicted would be sunny and have a ‘balmy’ high of 47°F (8°C) — would be a great day to try building a raised bed of my own at the edge of my garden.

Gathering Materials

Since I didn’t want to spend much money on my project, I decided to use what my land had in abundance: rocks. They’d been the best harvest from my soil for years, and I’d built an entire loose stone wall alongside my garden with them. Not wanting to cannibalize my wall, I decided to just walk up the wooded slope behind my garden and look for big rocks near the surface. I wanted a sturdy structure that wasn’t going to fall apart if I bumped into it, so I chose big rocks that were flat enough to be stacked.

For about three hours I pried these small boulders from the earth with a shovel and crowbar, and then carried or rolled them end over end to the edge of my garden area. After a winter of being cooped up, it was nice, exhausting work that left me feeling good at the end of the day. The only downside was getting a finger smashed between two big rocks, but after wrapping it up I was fine to continue.

If you don’t have stone on your property, you could use brick, cinder blocks, or just about anything else that’s sturdy enough. Since I had some old bricks I’d scavenged from a demolition site on hand, I decided to use these to pave my keyhole walkway. I also used cardboard from banana boxes I had lying around for a barrier between the ground and the soil of my raised bed, and an old weed liner to help keep the soil from moving out of any cracks.

Building

Step One: Measure and Mark.

Ignore the bricks. I was just experimenting to see
how they’d work as an edge, but discarded the
idea as unworkable

First, mark off your center spot with a stake. Measure a circumference around the stake based on your desired size and mark it in the dirt.

I ended up using the length of my arm as a basis for the circumference and added a few inches on top, but it’s up to you. My aim was to be able to reach any point of the raised bed from the keyhole, and this worked out.

You can mark off the dimensions easily using a measured piece of string tied to the center stake at one end and a second unburied stake at the other. Use the unburied stake to trace the line. I ended up planting four stakes around to mark off the circle.

At some part of the circle, measure two or three feet of the edge and mark it off. Draw a straight line from both ends of this to the center stake, or make a different design that you like. This will be your keyhole walk way.

Step Two: Clear the Ground

Although not everyone may need to do this, there are always a million roots and rocks under any patch of land I dig into. I opted to dig down about a foot and remove the big roots and rocks. I wanted to delay as long as possible any roots growing upward into my raised bed.

Step Three: Make a Trench

I’m not sure if it was necessary, but I figured putting the lowest layer of my rocks in a slight trench would add to the structural integrity of my raised bed.

I dug a shallow trench along the circumference of my circle and placed my flattest stones in it. This provided a stable base for the rest of my wall.

Step Four: Start Stacking

Now it’s just a matter of doing a good job stacking your rocks on top of each other. I was using large rocks, so the work was tiring but rewarding.

It may take some time to find the right rock for each spot, but when you’ve crafted a sturdy raised bed planter that’s not going anywhere, you’ll be pleased with the time you took.

My father, who has a good eye for this kind of work, came out and helped me with the stacking. We ended up breaking one of our rocks with a hammer to get it to lie flat and stable, but after finagling them around, most of the rocks worked without any alterations.

Step Five: Put in a Floor

You should apply the cardboard a bit thicker
than this photo shows

If you have polluted soil underneath your raised bed or something like pavement, adding in a permanent of semi-permanent floor can help separate your rich soil from whatever is below. This will also keep out roots and weeds. You could use stone or wood for a fairly permanent choice, or, like me, go with cardboard. Cardboard should last a few years and keep weeds in the ground from infiltrating your rich soil. When the cardboard does decay, it will only enrich your soil further.

You can see that at this point I also added an extra liner left over from a previous project because I thought the soil might pour out of cracks in the rock. It ended up being completely extraneous, and the soil stayed in place just fine on its own.

Step Six: Build the Keyhole

Most people will probably build the keyhole area from the same materials they used to build the rest of the raised bed, but since I had bricks on hand I decided to go with those. I could get away with this because I was building on a hill and I didn’t need to build as high in the back.

Bricks were also a bit easier to set into the ground for the tighter quarters of the keyhole walkway. I buried part of each brick in the ground to secure them.

Step Seven: Shovel in the Dirt

If you want to have a better yield than you’d find in the ground, you of course need superior soil to put in your raised bed.

I mostly used soil from my composter, which was made from grass, leaves, wood, food scraps, vegetation from the woods, etc. I also added in an 80 pound bag of cow manure I bought for $6 and a leftover bag of top soil that had been sitting around. Finally, I threw in a bit of peat moss.

I mixed it up and shoveled it in, and it has produced some delicious vegetables for me.

Step Eight: Getting Fancy

If you feel so inclined and you have the time, you can pave the keyhole area with rocks or bricks. I found this area sometimes got muddy when left unpaved, so I ended up putting the paving in so I could stand or kneel without getting covered in mud. I also added a second layer of bricks to the rear to make the back more sturdy.

Step Nine: Planting and Adapting

This photo was taken in spring with only about
a quarter of the space planted

Because the area I chose gets only about 4-6 hours of sunlight per day, depending on the time of year, I mostly grow leaf vegetables in my raised keyhole garden, but if you’ve got the sun, you can grow anything.

Of course, like so many plans, sometimes mother nature doesn’t play along. After having several crops decimated by deer coming out of the woods, I ended up using some stakes and plastic netting to keep them at bay. This does limit my ability to get into the garden a bit, but it hasn’t been a big problem.

I’ve gotten some great produce out of this project, and I’m very pleased I took the time to do it. The entire job took about 13 hours, with an additional few hours a while later to add in the brick paving to the keyhole.

I like the idea of this project because it’s so versatile. Whether you’re in a desert, an inner city with polluted soil and impermeable pavement, or anywhere in between, a raised bed keyhole garden can be a real asset.